1. Field of the Invention
This invention relates to ink jet inks for use in ink jet printers. More particularly, this invention relates to phase change, or hot melt, ink jet inks for use in ink jet printers from which ink is propelled from the printer nozzle by heat or by a pressure wave. Most particularly, the invention relates to hybrid polymers designed to contribute properties to the phase change ink which could not be gained if the polymers used to form the hybrid were added individually.
2. Description of Related Art (Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98)
Ink jet printing involves the placement in response to a digital signal of small drops of a fluid ink onto a surface to form an image without physical contact between the printing device and the surface. The method of drop generation varies among the different ink jet technologies and can be used to classify ink jet printing into two major technology types, continuous (CIJ) and drop-on-demand (DOD).
In CIJ printing systems, a continuous stream of liquid ink droplets is ejected from a nozzle and is directed, with the assistance of an electrostatic charging device in close proximity to the print head, either to a substrate to form a printed image or to a recirculating system. Inks for CIJ printing systems are typically based on solvents such as methyl ethyl ketone and ethanol.
In DOD ink jet printing systems, liquid ink droplets are propelled from a nozzle by heat (thermal or bubble ink jet) or by a pressure wave (piezo ink jet). Unlike CIJ systems, all the ink droplets are used to form the printed image and are ejected when needed, xe2x80x9con demand.xe2x80x9d No deflection of ink droplets is involved. Thermal or bubble ink jet inks typically are based on water and glycols. Piezo ink jet systems generally use aqueous, solvent, or solid inks. These last inks, also known as phase change inks, are solid at ambient temperature and liquid at printing temperatures. It is these inks to which the present invention relates.
The following properties are required of an ink composition for ink jet printing:
(a) high quality printing (edge acuity and optical density) of text and graphics on substrates, in particular, on uncoated cellulosic paper,
(b) short dry time of the ink on a substrate and good adhesion such that after printing the print is not smudged when rubbed or offset onto a subsequent printed image placed upon the print,
(c) good jetting properties exhibited by a lack of deviation of ink droplets from the flight path (misplaced dots) and of ink starvation during conditions of high ink demand (missing dots),
(d) resistance of the ink after drying on a substrate to water and to solvents,
(e) long-term storage stability (no pigment settling) and
(f) long-term reliability (no corrosion or nozzle clogging).
Inks are known that possess one or more of the above listed properties. However, few inks are known that possess all of the above listed properties. Often, the inclusion of an ink component meant to satisfy one of the above requirements can prevent another requirement from being met. For example, the inclusion of a polymer in the ink composition can improve the adhesion of the ink to the substrate. However, the polymer can impair the jetting of the ink because of the behavior of the polymer under the high shear conditions of jetting (104-106 secxe2x88x921). Thus, most commercial ink jet inks represent a compromise in an attempt to achieve at least an adequate response in meeting all of the above listed requirements.
The use of polymers in phase change (hot melt) inks and the printing of such inks has been disclosed in the following publications:
U.S. Pat. No. 5,006,170 teaches the use of xe2x80x9crosin estersxe2x80x9d with a colorant and a propellant.
U.S. Pat. No. 5,531,819 teaches the use of an xe2x80x9cacrylic resin,xe2x80x9d xe2x80x9crosin resin,xe2x80x9d xe2x80x9chydrogenated rosin resin,xe2x80x9d xe2x80x9cpetroleum resin,xe2x80x9d xe2x80x9chydrogenated petroleum resin,xe2x80x9d xe2x80x9cor xe2x80x9cterpene resinxe2x80x9d with a wax, a colorant, and a plasticizer.
U.S. Pat. No. 5,354,368 discloses the use of a xe2x80x9ctall oil rosin having a high acid numberxe2x80x9d with a rheology modifier. Given as examples of xe2x80x9ctall oil rosinxe2x80x9d are xe2x80x9cnatural tall oil and wood rosins as well as modified tall oil and wood rosins and tall oil and wood rosin derivatives.xe2x80x9d
U.S. Pat. No. 5,397,388 teaches the use of xe2x80x9cacrylic resin,xe2x80x9d xe2x80x9crosin resin,xe2x80x9d xe2x80x9cpetroleum resin,xe2x80x9d xe2x80x9cmodified petroleum resin,xe2x80x9d xe2x80x9chydrogenated petroleum resin,xe2x80x9d or xe2x80x9cterpene resin,xe2x80x9d with a wax, an organic substance miscible with the wax, and a colorant.
U.S. Pat. No. 5,409,530 teaches the use of a resin selected from the group consisting of xe2x80x9crosins, rosin derivatives, terpenes, [or] modified terpenes . . . xe2x80x9d with a second component to dissolve the resin.
U.S. Pat. No. 5,514,209 discloses the use of a xe2x80x9cglycerol ester of a hydrogenated rosinxe2x80x9d with a microcrystalline wax.
U.S. Pat. No. 5,620,508 teaches the use of xe2x80x9crosin-type resinsxe2x80x9d with pigments and oil-soluble dyes. Given as examples of rosin-type resins are xe2x80x9crosins, hydrogenated rosins, disproportionated rosins, rosin esters, rosin-modified phenolic resins, rosin-modified maleic acid resins, and rosin-modified xylene resins.
Also, EP 0 739 958 A2 teaches the use of an xe2x80x9cacrylic resin,xe2x80x9d rosin resin,xe2x80x9d xe2x80x9cpetroleum resin,xe2x80x9d xe2x80x9cmodified petroleum resin,xe2x80x9d xe2x80x9chydrogenated petroleum resin,xe2x80x9d or xe2x80x9cterpene resin,xe2x80x9d with at least one wax, a colorant, and a second resin. One resin has a softening point from room temperature to 100xc2x0 C., and the other resin has a softening point from 50-150xc2x0 C.
While the prior art teaches the use of many classes of polymers in phase change (hot melt) inks, the ability of using different classes of polymers within the same ink composition can be limited due to compatibility of the polymers with each other. Furthermore, printed images made with inks that contain certain- polymers that have poor quality images and lack scratch resistance, low-temperature storage stability and flexibility, offset and pick resistance, adhesion, and other desired properties.
The essential component of the present invention is a hybid polymer. This polymer is prepared by chemically attaching one class of polymer to another. For example, a useful polymer is one that has an acrylic polymer attached to a rosin polymer. The novel aspect of using a hybrid polymer in a phase change (hot melt) ink is that it allows two polymers that are incompatible when added individually in the ink composition to be rendered compatible in the ink composition when used in the state in which the polymers are chemically joined together. This allows the unique property enhancing attributes of two incompatible polymers to be exploited in the same ink composition. Such hybrid polymers suitable for phase change (hot melt) inks are unknown. Hybrid polymers can be used as the sole polymer of the ink composition, in combination with other hybrid polymers, or in combination with other polymers.
In accordance with the present invention, the preparation of phase change (hot melt) inks useful in ink jet printing devices is provided. The phase change (hot melt) inks preferably are for use in a piezo ink jet printer with which recording is conducted by thermally melting an ink composition at a temperature above ambient temperature (20xc2x0 C.) and then ejecting the ink composition onto a porous or non-porous substrate such as paper, aluminum, glass, metal, wood, synthetic polymer films, and textiles. Furthermore, the present invention also provides methods for the preparation of hybrid polymers and for their use-in the above-described inks.
The present invention overcomes many of the problems associated with the use of prior art phase change(hot melt) ink compositions while achieving distinct advantages thereof. Accordingly, an object of the present invention is to provide improved ink compositions capable of satisfying simultaneously the properties required of an -ink composition for ink jet printing, especially the aforementioned properties (a) to (f) and which comprise a hybrid polymer. Other objects and advantages of the present invention will become apparent from the following disclosure.
In accordance with the present invention, the preparation of phase change (hot melt) inks useful in ink jet, hot melt gravure, and similar printing devices is provided. The phase change (hot melt) inks preferably are for use in a phase change (hot melt) ink jet recording device in which recording is conducted by thermally melting the ink at a temperature above ambient temperature (20xc2x0 C.) to provide prints that possess high quality images, scratch resistance, abrasion resistance, low-temperature storage stability and flexibility, offset and pick resistance, adhesion, and other desired properties. Furthermore, the present invention also includes methods for the preparation of hybrid polymers and for their use in the above-described inks.
In accordance with the present invention, the ink compositions comprise:
(a) from about 0.1% to about 30% of one or more colorants; and
(b) from about 0.1 to about 99.9% of one or more hybrid polymers.
Components other than those listed above may be included in the ink compositions to achieve specific printer, substrate, or end use requirements.
The phase change (hot melt) inks of the present invention comprise a colorant and a hybrid polymer. Other components that may be added, include but are not limited to, waxes, polymers, antioxidants, biocides, and corrosion inhibitors.
Coloring agents that may be incorporated in the ink composition include pigments and dyes. Any dye or pigment or combination of one or-more dyes or pigments may be used as long as the colorant can be dispersed in the ink composition and is compatible with the other components of the composition. The coloring material of the present invention is preferably a pigment.
No particular limitation is imposed on the type or the amount of pigment used. The term xe2x80x9cpigmentxe2x80x9d refers to a solvent insoluble colorant. A large range of pigments, organic and inorganic, may be used either alone or in combination. Pigments used in ink jet inks typically are in the dispersed state and are kept from agglomerating and settling out of the carrier medium by placing acidic or basic functional groups on the surface of the pigments, attaching a polymer onto the surface of the pigments, or adding a surfactant to the ink.
The amount of the pigment present in the ink compositions is from about 0.1 to 30 wt %, preferably from about 2 to 10 wt %. Examples of a pigment that may be used in the practice of the present invention for a yellow ink include C.I. Pigment Yellow 1, C.I. Pigment Yellow 3, and C.I. Pigment Yellow 13. Examples of a pigment that may be used in the present invention for a magenta ink include C.I. Pigment Red 5, C.I. Pigment Red 7, C.I. Pigment Red 12, C.I. Pigment Red 112, and C.I. Pigment Red 122. Examples of a pigment that may be used in the present invention for a cyan ink include C.I. Pigment Blue 1, C.I. Pigment Blue 2, C.I. Pigment Blue 16, C.I. Vat Blue 4, and C.I. Vat Blue 6.
The pigment particles need to be small enough in size so that they move freely through the printing device. Because the ejecting nozzles of ink jet ink printers range in diameter from about 10 to 100 microns, pigments suitable for use in the present invention may have a range of particle sizes from about 0.01 microns to 100 microns, preferably from about 0.01 microns to 10 microns, and more preferably from about 0.01 microns to 5 microns.
No particular limitation is imposed on the type or the amount of dye used. Dyes which are useful in the present invention are those which are water soluble or water-insoluble such as basic, acid, and direct dyes. If desired, the dyes can be reactive dyes which contain groups capable of forming covalent bonds with textile materials. The amount of dye present in the ink compositions is from about 0.1 to 30 wt %, preferably from about 2 to 10 wt %.
Fine particles of metal or metal oxides also may be included as colorants for the compositions of the present invention. Metal and metal oxides are used in the preparation of magnetic ink jet inks. Examples may include silica, alumina, titania, and finely divided copper.
The essential component of the present invention is a hybrid polymer. This polymer is prepared by chemically attaching one class of polymer to another. The novel aspect of using a hybrid polymer in a phase change (hot melt) ink is that it allows two polymers that are incompatible in the ink formulation to be rendered compatible in the ink formulation when use in the state in which the polymers are chemically joined to each other. This allows the unique property enhancing attributes of two incompatible polymers to be exploited in the same ink composition. Hybrid polymers can be used as the sole polymer of the ink formulation or in combination with other polymers, including other hybrid polymers.
The polymers suitable for use in the present inventions may include naturally occurring polymers such as alginic acid, carboxymethyl cellulose, starch, shellac, and pectinic acid; synthetic analogues of naturally occurring polymers such as hydroxyalkyl starch, rosin esters, lignosulfanates, nitrocellulose, alkyl celluloses, aryl celluloses, cellulose esters, cellulose ethers, chitin, chitosan, and polysaccharides; synthetic polymers such as polyamid, polyacrylamide, polyacrylic acid, polyethylene oxide, polyethylene glycol, polyethyleneimine, polymethacrylic acid, polyitaconic acid, polymaleic acid, polyvinyl alcohol, cyclopentadiene resin, polyurethane, poly (N-vinylpyrrolidinone), polynorbornadiene, poly (ethylene maleate), hydroxy-terminated polybutadiene, polyallylamine, carboxyl-terminated polybutadiene, and polyvinyl methyl ether; and synthetic copolymers such as styrene/acrylic acid, styrene/maleic anhydride, styrene/allyl alcohol, acrylamide/acrylic acid, ethylene/vinyl acetate, acrylic acid/N-vinyl pyrrolidinone, hydrocarbon/tall oil resin, phenol/formaldehyde, glycidyl methacrylate/vinyl acetate, epoxy/novolac, epoxy/acrylate, urethane/acrylate, amine-terminated poly(butadiene/acrylonitrile), poly(butadiene/maleic anhydride), cyclopentadiene/indene, and vinylnaphthalene/itaconate copolymers. The copolymers may be block, graft, tapered, branched, and random copolymers. Methods of polymerization include solution, emulsion, suspension, and bulk polymerization. While physical properties of the polymers can be affected by the polymerization method, the resultant polymers can provide the desired outcomes of the invention.
No particular limitation is imposed on the physical properties of the polymers. Preferred polymers are those having an acid number in the range of from about 10 to 300, a weight average molecular weight in the range of from about 500 to 250,000, a softening point in the range of from about 0 to 150xc2x0 C., and a glass transition temperature of in the range of from about xe2x88x9225 to 180xc2x0 C. More preferred polymers are those having an acid number in the range of from about 20 to 80, a weight average molecular weight in the range of from about 2000 to 35,000, a softening point in the range of from about 40 to 90xc2x0 C., and a glass transition temperature from about 25 to 80xc2x0 C.
Any one of known waxes may be used in the phase change (hot melt) ink formulation with no particular restriction. A preferred wax is solid at room temperature and is molten sufficiently at the operating temperature of the printing device. Examples of suitable waxes include petroleum waxes, such as paraffin wax and micro crystalline wax; plant waxes, such candelilla wax and carnauba wax; animal waxes, such as bees wax and lanolin; synthetic hydrocarbon waxes, such as a Fisher-Tropsch wax and a polyethylene wax; higher fatty acids, such as stearic acid and lauric acid; higher alcohols, such as stearyl alcohol and 12-hydroxystearic acid; and derivatives thereof and combinations thereof. These waxes may be used alone in the ink formulation or admixed with one or more other waxes.
Polymers used in phase change (hot melt) inks of the present invention generally have melting points in the range of about 40xc2x0 C. to 200xc2x0 C., and preferably from about 60xc2x0 C. to 140xc2x0 C. The polymer should be thermally stable in a molten state so that gaseous products are not generated or deposits on the printer device are not formed.
Examples of suitable polymers for ink compositions of the present invention include, but are not limited to, one or more of the following: alkyd resins; amides; acrylic polymers; benzoate esters; citrate plasticizers; cumarone-indene resins; dimer fatty acids; epoxy resins; fatty acids; ketone resins; maleate plasticizers; long chain alcohols; olefin resins; petroleum resins; phenolic resins; phthalate plasticizers; polyesters; polyvinyl alcohol resins; rosins; styrene resins; sulfones; sulfonamides; terpene resins; urethanes; vinyl resins; and derivatives thereof and combinations thereof. No limitation is placed on the type or the amount of the polymer that is present in the ink.
Phase change (hot melt) ink compositions prepared in accordance with the present invention are in a molten state during printing. To prevent thermally induced oxidation from occurring in this state, antioxidants may be added to the ink composition. Suitable antioxidants, present preferably in the amount of about 0.1% to 1.0% by weight of the ink composition, include, for example, Irganox(copyright) 1010 (Ciba-Geigy Corp.).
To prevent the growth of microorganisms, a biocide may be added, preferably in the range of about 0.01% to 5%, based on the weight of the ink composition. Examples of suitable biocides include sorbic acid, vinylenebis-thiocyanate, bis(trichloromethyl)sulfone, and zinc pyridinethione.
One or more corrosion inhibitors may be added to inhibit the corrosion of the metal that comes in contact with the phase change (hot melt) ink. Suitable corrosion inhibitors, present preferably in the range of about 0.1% to 5% (based on the weight of the ink composition), include ammonium dinonyl naphthalene sulphonate.
No limitation is placed on the way in which the components of the phase change (hot melt) ink compositions of the present invention are combined in the preparation of the compositions. A preferred method involves adding all the components, except the colorant and the hybrid polymer, heating the components at about 135xc2x0 C., while slowly stirring, until a homogenous mixture is obtained. Then, under the same conditions, the hybrid polymer is added at a rate such that a homogenous mixture is obtained. In this manner, more of the hybrid polymer can be incorporated into the ink composition. The coloring agent (pigment) is subsequently added and stirring and heating are continued until the colorant is properly dispersed. If a greater degree of dispersion is desired, a dispersing machine such as a three roll mill, an attritor, a ball mill, or a colloid mill can be used. The molten mixture is then filtered to remove particles of a size too large for effective printing.
Inks suitable for use with phase change (hot melt) ink jet printers should be solid at room temperature, by which is meant about 18xc2x0 C. to about 27xc2x0 C., and are transformed into a molten state at temperatures ranging from 45xc2x0 C. to 150xc2x0 C. Most preferably these inks should melt from about 65xc2x0 C. to 130xc2x0 C. The phase change inks also should exhibit a relatively low melt viscosity of 1 to 50 cP between 100xc2x0 C. and 150xc2x0 C., most preferably 5 to 20 cP. The inks also should exhibit excellent dispersion and stability of this dispersion, especially when exposed to the elevated temperatures at which the ink is commonly stored and jetted in the printing device. The ink compositions of the present invention meet the aforementioned requirements.
Inks suitable for use with hot melt (phase change) ink jet printers should provide prints with excellent quality (good edge acuity and high optical density), and there should be no missing or misplaced dots. The inks should dry quickly onto the printed substrate as well as adhere well to said substrate to provide a print with resistance to abrasion, water, and solvents. The ink compositions of the present invention meet these requirements.
The ink compositions of the present invention possess desirable non-Newtonian properties. That is, these inks exhibit a relatively high viscosity at relatively low shear rates, e.g., 12 cP or more, but a much reduced viscosity at relatively high shear rates, e.g., 104 secxe2x88x921 or more. The high viscosity at low shear helps to keep the colorant in suspension when the ink is being stored whereas the low viscosity at high shear reduces the energy required to eject the ink droplet from the printhead.
The compositions of the present invention may be used in phase change (hot melt) ink jet, hot melt gravure, and similar printing methods. A preferred method of printing involves phase change (hot melt) ink jet printing using piezo ink jet printers. The specific ink jet printer employed is not critical.
No limitation is placed on the substrate that can be used in the practice of the present invention. The compositions of this invention can be applied to a wide range of porous and non-porous substrates such as paper, aluminum, glass, metal, wood, synthetic polymer films, and textiles. The temperature of the substrate can be adjusted to improve properties such as print quality and adhesion. For example, the substrate can be passed through heated rollers subsequent to printing to improve print quality by increasing dot gain. Also, the temperature of the ink ejected from the printer can be raised so that when it comes into contact with a compliant substrate, such as plastic, enhanced adhesion can occur due to partial fusing.
Specific embodiments of the phase change (hot melt) inks of the present invention are provided in further detail herein below. These examples are intended to be illustrative, and the invention is not limited to the materials set forth in these embodiments. All parts are by weight unless otherwise noted.